The Principal Investigators have undertaken to organize the Fourth HLA and Cloning Workshop at the request of the membership made at the Third Workshop Meeting in Strasbourgh, France, May, 1984. The purpose is to bring together an international group of investigators studying the genes and gene products of the murine and human major histocompatibility complexes. Representatives of each of the laboratories engaged in this research will meet for two and one-half days to discuss and analyze their latest research. These results will span the entire range of applications of molecular biology to the structure, function, expression, regulation and mechanism of action of the gene products of the human and murine MHCs. It is anticipated that major new findings on the genetic organization of the human MHC, the molecular mechanisms of regulation of expression of Class I and Class II MHC genes, the primary, secondary (and perhaps tertiary) structure of MHC gene products, the use of transfection and site specific mutagenesis, and extensive and detailed studies of restriction fragment length polymorphism and allelic structural variation in the HLA DR, DC and SB alpha and beta chain genes will be presented. It is also expected that numerous reports of the association of particular subtypes of HLA DR, DC and SB alpha and beta alleles with particular diseases will be reported. This meeting will be one of the first to begin to consider ways of altering the function or expression of MHC gene products involved in susceptibility or resistance to a wide variety of diseases. Diseases to be considered will include rheumatic (rheumatoid arthritis, ankylosing spondylitis), neurologic (multiple sclerosis and myasthenia gravis), endocrine (Type I diabetes mellitus, hyperthyroidism and Addison's disease), autoimmune (Goodpasture's syndrome, chronic active hepatitis, Lyme arthritis), dermatologic (Behcet's disease, psoriasis), and gastrointestinal (celiac disease, chronic active hepatitis) disease. Laboratories studying altered or increased expression of Class II MHC gene products in viral and carcinogen-induced experimental tumors will be invited to present their results. The role of MHC genes in susceptibility to autoimmune diseases and in resistance to neoplasia will be discussed at the molecular level. Sessions on methods of altering function of MHC genes are planned to develop new types of immunologic therapy.